This invention relates to a process for making agglomerates of porous aluminium oxide and, in particular, to a process for making agglomerates of porous aluminium oxide from a hydrous aluminium oxide gel.
A process similar to that disclosed in the present specification is discussed in Netherlands Patent Application No. 6,604,215, which corresponds to British Pat. No. 1,129,980. In said reference, aluminium oxide agglomerates are obtained by drying an amorphous hydrated aluminium oxide slurry very rapidly and under such conditions that the amorphous state of the resulting fine powder is maintained. Subsequently, the powdered aluminium oxide is wetted with water or an ammonia solution and subsequently agglomerated. The agglomerates are then aged and calcined. The disadvantage of such a process is primarily that the aluminium oxide must first be dried and then subsequently rewetted, thus causing great processing time to be assumed.
Also, from the Journal of Catalysis, Volume 10, pages 342-354, 1968, and from U.S. Pat. No. 3,577,353, it is known that the direct drying of an aluminium oxide gel leads to severe shrinkage of said gel. The resulting high attraction between the gel particles may be attributed to the relatively high surface tension of the water contained in said gel. Consequently, after the gel has been dried, compact aluminium oxide, having a low pore volume, will be obtained. From the Journal reference and U.S. Pat. No. 3,577,353, it is also known that the shrinkage may be very much reduced by bringing the gel into contact with such an amount of an organic liquid that water contained in the gel is essentially replaced by the organic liquid, in its entirety. The only criterion which the organic substance must exhibit, according to the references, is that it has a lower surface tension than water. Methanol and ethanol, which are both water-miscible substances, are disclosed as being most suitable for such a purpose. Drying a gel treated in the foregoing manner leads to a powdered aluminium oxide having a relatively low density and a high porosity. Thus, the foregoing process does not produce agglomerates of aluminium oxide, but rather powders thereof.
U.S. Pat. No. 3,801,705 discloses a process similar to the foregoing, but relating to the preparation of silica gels, in which process there is utilized an organic solvent which is immiscible with water.